A series of x-ray diffraction experiments are planned to determine the projected, cross-sectional density profile of the retinal rod photoreceptor disk membrane on an absolute scale, using data out to (1/10A). We will employ a novel oscillation camera for isolated rod outer segments to maximize the scattering information recorded with a fixed data-collecting time interval. We will examine the structural effects of bleaching on the photoreceptor membrane by x-ray diffraction techniques, and follow the accompanying changes in birefringence. In order to interpret the electron density profiles obtained, we make use of published data on chemical composition, covalent labeling and enzymatic degradation studies. In addition, we are undertaking: a) low-angle solution scattering studies on rhodopsin-detergent complexes; b) studies on isolated disks, with and without prior enzymatic degradation of rhodopsin; and, c) examination of recombination lipid-rhodopsin membranes by x-ray diffraction techniques and Dichroic Absorption Studies. We will extend our previous x-ray diffraction studies on retinal rods at liquid N2 temperatures to determine the specimen freezing procedures which best preserve in vivo parameters. By using this established method, we will then freeze-fracture the samples, and replicate the surfaces in a system designed to minimize contamination and surface temperature changes. The aim of these studies is to provide information necessary for evaluating the particles seen on the A fracture face, and for assessing the distribution of rhodopsin in the disk membrane. Lastly, we plan a series of experiments to localize calcium in rod outer segments and to follow its redistribution with bleaching. Preliminary studies will also be carried out on the calcium-bindings binding properties of the interdisk cytoplasmic gel. The long range goal of these studies is the elucidation of the intermediate molecular mechanisms involved in photoexcitation.